Production of hydroxyphenylpropionic acid ester having a novel crystalline structure

ABSTRACT

3,9-bis{2-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl) propionyloxy]-1,1-dimethylethyl}-2,4,8,10-tetraoxaspiro[5.5] undecane having a novel crystalline structure which, when subjected to Cu-K.sub.α X-ray diffraction, shows sharp X-ray diffraction peaks at angles of diffraction, 2θ=4.2° and 2θ=10.6°. Also provided is a method for producing this compound, using a certain recrystallization solvent.

This application is a division of Ser. No. 868,743 filed May 30, 1986,now U.S. Pat. No. 4,769,479.

The present invention relates to3,9-bis{2-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1-dimethylethyl}-2,4,8,10-tetraoxaspiro[5.5]undecane(hereinafter referred to as hydroxyphenylpropionic acid ester)represented by the structural formula (I) having a novel crystallinestructure: ##STR1##

It is well known that the hydroxyphenylpropionic acid ester representedby the structural formula (I) can effectively be used to prevent variouskinds of synthetic resin from deterioration such as softening,embrittlement, surface crack, discoloration, etc. caused by the actionof heat, light and oxygen at the time of processing and use [JapanesePatent Application Kokai (Laid-Open) Nos. 25826/1984 and 231089/1984].As such synthetic resins, there may be mentioned polyolefins such aspolyethylene, polypropylene, etc., styrene series synthetic resins suchas polystyrene, impact-resistant polystyrene, ABS, etc., engineeringplastics such as polyacetal, polyamide, etc., and polyurethane.

Previously, the present inventors found that the hydroxyphenylpropionicacid ester represented by the structural formula (I) exists in twoforms, one being in the form of a glassy substance having a meltingpoint of about 45° C. to about 55° C. (hereinafter referred to asγ-crystal) and the other being in the form of white crystals having amelting point of about 104° C. to about 109° C. (hereinafter referred toas αβ-crystal).

The γ-crystals were obtained by melting a mixture of the ester (I) andimpurities resulting from the production reaction, or the ester (I) ofimproved purity obtained by purification by column chromatography, etc.,and then rapidly cooling the melt without using a solvent, and themelting point was in the range of from about 45° C. to about 55° C. TheCu-K₆₀ X-ray diffraction pattern of the γ-crystals was as shown in FIG.4.

The αβ-crystals were obtained when the recrystallization method withn-hexane for3,9-bis{2-[3-(3,5-ditert-butyl-4-hydroxyphenyl)propionyloxy]-1,1-dimethylethyl}-2,4,8,10-tetraoxaspiro[5.5]undecanerepresented by the structural formula (II) (disclosed in the foregoingJapanese Patent Application Kokai No. 25826/1984), ##STR2## having asimilar structure to that of the hydroxyphenylpropionic acid ester ofthe present invention represented by the foregoing structural formula(I), was applied as such to said ester (I), and the melting point was inthe range of from about 104° C. to about 109° C. the Cu-K₆₀ X-raydiffraction pattern of the αβ-crystals was as shown in FIGS. 2 and 3.Generally, the αβ-crystals seem to be obtained as a mixture of two ormore forms having different crystalline structures, and the X-raydiffraction pattern varies as shown by FIGS. 2 and 3 depending upon themixing ratio of the different forms. The melting point of the crystalssometimes is lowered a little or becomes wide in its range by reductionin purity, like usual compounds.

Thus, the present inventors' study has shown that thehydroxyphenylpropionic acid ester represented by the structural formula(I) takes either one of the αβ- or γ-crystal structure, and those otherthan these crystalline structures have not been known.

However, in producing these αβ- and γ-crystals on commercial scales,there have been many difficult problems, and only unsatisfactory resultshave been obtained.

For example, in the production of the αβ-crystals with, particularly,n-hexane as a recrystallization solvent, scaling of therecrystallization apparatus is remarkable, and also the purificationeffect is low because of a small solubility difference between the esterof the structural formula (I) and impurities contained in the mixture tobe purified. This recrystallization method was therefore disadvantageousto use in commercial-scale purification.

With respect to the γ-crystals, the purification effect cannot beexpected at all from the mixture of said ester (I) and impurities whichresults from the production reaction. Column chromatography is effectiveas a purification method, but it cannot be used as a large-scalecommercial purification method for economical reasons.

It has therefore been considered to be very difficult to produce thehydroxyphenylpropionic acid ester represented by the structural formula(I) with ease and in high purity on a commercial scale.

The present inventors have extensively studied to solve these problems,and as a result, found that by carrying out the crystallization under aspecific condition using a specific recrystallization solvent, thehydroxyphenylpropionic acid ester represented by the structural formula(I), with excellent quality and completely different in the crystallinestructure from the conventional ones, can be obtained simply andeconomically, and also that the crystals thus obtained are higher in themelting point than the αβ- and γ-crystals, so that they can be used moreadvantageously. The present inventors have thus attained the presentinvention.

Thus the present invention is to provide the hydroxyphenylpropionic acidester represented by the structural formula (I) having a novelcrystalline structure which shows sharp X-ray diffraction peaks atangles of diffraction, 2θ=4.2° and 2θ=10.6°, in Cu-K₆₀ X-raydiffraction, and also to provide an advantageous method for producingsaid ester on a commercial scale.

The hydroxyphenylpropionic acid ester of the present inventionrepresented by the structural formula (I) having a novel crystallinestructure (hereinafter referred to as δ-crystal) has a diffractionpattern as shown in Table 1 and FIG. 1, in Cu-K.sub.α X-ray diffraction.

The δ-crystals of the present invention have a melting point in therange of from about 124° C. to about 127° C., and its Cu-K.sub.α X-raydiffraction pattern, shown in Table 1 and FIG. 1, has sharp diffractionpeaks, particularly, at 2θ=4.2° and 2θ=10.6°, for which reason thecrystals can easily be distinguished from the αβ- and γ-crystals. Themelting point of the δ-crystals, of course, sometimes is lowered alittle below or the range becomes wider than the melting point rangedescribed above, by reduction in purity like usual compounds, and it isgenerally in the range of from 118° C. to 126° C. when prepared by theδ-crystal production method of the present invention to be describedbelow.

The δ-crystals of the present invention, because of the higher meltingpoint than that of the α,β-crystals, shows an improved blocking propertyat the drying and crushing steps subsequent to the recrystallizationstep. The δ-crystals, surprisingly, have a lower solubility than that ofthe αβ-crystals (Table 2), and the compatibility with impuritiesproduced at the same time by the production reaction is low so that therecrystallization yield is high and a high-purity product can beobtained easily. Further, the growth of the δ-crystals is easy ascompared with the αβ-crystals, for which reason the δ-crystals can beobtained in large size crystals and have much improved filterability.

The foregoing excellent characteristics, and of course the presence ofthe δ-crystals of the present invention, could not be forecast from theprior art at all.

                  TABLE 1                                                         ______________________________________                                        Angle of diffraction                                                                             Relative                                                   No.         2θ (degree)                                                                        strength (%)                                           ______________________________________                                         1          4.16       96                                                      2          10.63      22                                                      3          11.36      4                                                       4          12.31      6                                                       5          12.67      6                                                       6          13.47      4                                                       7          14.91      65                                                      8          16.48      100                                                     9          16.92      64                                                     10          18.03      46                                                     11          19.11      13                                                     12          19.91      27                                                     13          20.94      27                                                     14          22.10      11                                                     15          23.70      10                                                     16          24.76      3                                                      17          26.12      12                                                     18          27.83      3                                                      19          28.83      8                                                      20          29.89      5                                                      21          31.74      4                                                      22          33.21      6                                                      23          35.47      5                                                      24          36.54      5                                                      25          38.06      3                                                      26          39.40      3                                                      27          41.58      4                                                      28          44.10      4                                                      29          45.57      4                                                      30          46.83      4                                                      ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        Solubility (g/100 g cyclohexane)                                              Temperature                                                                   (°C.)  αη-Crystal                                                                     δ-Crystal                                      ______________________________________                                        20            0.2        0.06                                                 30            0.5        0.1                                                  40            1.4        0.2                                                  50            4.1        0.5                                                  55            8.5        1.1                                                  60            >60        2.1                                                  ______________________________________                                    

The δ-crystals can easily be produced, for example, by dissolving thehydroxyphenylpropionic acid ester represented by the structural formula(I) in

(1) a recrystallization solvent comprising a water-soluble solvent andwater in an amount of 0 to 3 times by weight based thereon, or

(2) a recrystallization solvent comprising a C₅ -C₁₀ alicyclichydrocarbon,

and forming the crystals at a temperature of 40° C. or higher.

For the recrystallization, either one of (1) or (2) may be used. Whenthe recrystallization solvent (1) is used, it may be a water-solublesolvent alone. However when water is mixed with such solvent thesolubility can be lowered so that a temperature at which only theδ-crystals are formed may be further increased, as a result of which thegrowth of the crystals may be promoted and the filterabilty thereof canbe improved.

Also, such mixing of water causes a reduction in the solubility toincrease the crystallization yield, and in addition, is useful inimproved safety against ignition and explosion. Consequently, suchmixing of water is preferred industrially. The amount of water to bemixed varies depending upon the particular kind of solvent, but it isgenerally not more than 3 times by weight based on the water-solublesolvent. When the amount of water exceeds 3 times byweight, there is atendency for the quality of the product such as purity, color, etc. tolower remarkably.

The water-soluble solvents to be used include alcohols, glycols,aliphatic ketones, aliphatic nitriles, alicyclic ethers, amides,tertiary amines, etc.

The recrystallization solvent wherein the water-soluble solvent is usedwill be explained below in more detail.

The alcohols are preferably those having 1 to 8 carbon atoms, andparticularly preferably those having 1 to 3 carbon atoms. The amount ofwater to be mixed is preferably 0 to 0.4 time by weight based on thealcohol. Specific examples of the alcohol include methanol, ethanol,n-propanol, iso propanol, n-butanol, n-hexanol, 2-ethylhexanol,glycerin, etc., among which methanol and isopropanol are particularlypreferred. The amount of water to be mixed is particularly preferably 0to 0.3 time by weight for methanol, and 0 L to 0.2 time by weight forisopropanol.

The glycols are preferably those having 2 to 6 carbon atoms, andspecific examples include ethylene glycol, trimethylene glycol,diethylene glycol, triethylene glycol, etc. The amount of water to bemixed is preferably 0 to 0.3 time by weight based on the glycol.

The aliphatic ketones are preferably those having 3 to 6 carbon atoms,and specific examples include acetone, methyl ethyl ketone, diethylketone, methyl isobutyl ketone, etc., among which acetone isparticularly preferred. The amount of water to be mixed is preferably 0to 2 times by weight based on the ketone.

The aliphatic nitriles include acetonitrile, propionitrile, etc., andthey are preferably mixed with water in an amount of 0 to 1 time byweight based on the nitrile.

Alicyclic ethers include 1,4-dioxane, tetrahydrofuran, etc., the amidesinclude N,N-dimethylformamide, N,N-dimethylacetamide,N-methyl-2-pyrrolidone, etc., and the tertiary amines includetriethylamine, pyridine, etc. These solvents are preferably mixed withwater in an amount of 0 to 3 times by weight based thereon.

Also, C₅ -C₁₀ alicyclic hydrocarbons can be used alone as therecrystallizaton solvent, and their specific examples includecyclopentane, cyclohexane, methylcyclohexane, cyclooctane, cyclodecane,etc.

When any of the foregoing recrystallization solvents (1) and (2) isused, the temperature at which the crystals are formed is veryimportant, and the temperature for the crystallization should be 40° C.or higher.

When the temperature is lower than 40° C. the desired δ-crystals are notobtained in a good yield and the purity is low, because the formedcrystals are αβ-crystals only or a mixture of the αβ- and δ-crystals. Inorder to minimize the loss of the ester of the structural formla (I)remaining dissolved in the recrystallization solvent, it is of courseallowable that the solution after the crystallization at a temperatureof 40° C. or higher has substantially been finished is cooled far belowsaid temperature and filtered.

The δ-crystals can also be produced by recrystallizing thehydroxyphenylpropionic acid ester represented by the structural formula(I) from a mixed solvent comprising a water-insoluble solvent exceptalicyclic or aliphatic hydrocarbons and an aliphatic hydrocarbon in anamount of 0 to less than 10 times by weight based on the water-insolublesolvent.

The water-insoluble solvent other than alicyclic or aliphatichydrocarbons, as referred to herein, includes esters, aliphatic ethers,aliphatic halides, aromatic chlorides, aromatic hydrocarbons, etc. Morespecifically, there may be mentioned esters such as ethyl acetate,n-butyl acetate, dimethyl phthalate, di-n-butyl phthalate, etc.,aliphatic ethers such as diethyl ether, diisopropyl ether, etc.,aliphatic halides such as chloroform, carbon tetrachloride,1,2-dichloroethane, 1,1,2,2-tetrachloroethane, etc., and aromaticchlorides such as chlorobenzene, dichlorobenzene, etc. Also, as thearomatic hydrocarbons, those having 7 to 12 carbon atoms are preferred,and specifically, there are given toluene, o-xylene, m-xylene, p-xylene,1,2,3-trimethylbenzene, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene,1,2,4,5-tetramethylbenzene, ethylbenzene, cumene, o-cymene, m-cymene,p-cymeme, o-diisopropylbenzene, m-diisopropylbenzene,p-diisopropylbenzene, etc.

When such water-insoluble solvent is used as the recrystallizationsolvent, the solubility of the αβ-crystals in this solvent is so highthat the δ-crystals containing substantially no αβ-crystals can beobtained even at room temperature. Thus in this case, the temperature atwhich the crystals are to be formed is not particularly limited. In thiscase, by using the water-insoluble solvent in mixture with an aliphatichydrocarbon in an amount of 0 to less than 10 times by weight basedthereon, the solubility of the δ-crystals can be lowered, so that itbecomes possible to carry out the crystallization at a highertemperature and also the crystallization yield can be increased. As suchaliphatic hydrocarbon, those having 6 to 10 carbon atoms are preferred,and specifically, there may be exemplified n-hexane, n-heptane,n-octane, 2-methylheptane, n-decane, etc.

In any of the methods described above, the amount of therecrystallization solvent to be used is generally 0.5 to 10 times byweight based on the material to be subjected to the crystallization.

Recrystallization is carried out by completely dissolving the startingcompound in the recrystallization solvent at the boiling point or atemperature lower than that, adding seed crystals as nucleus forcrystallization if necessary, at a temperature corresponding to thesolvent and then stirring the solution at the same temperature to formthe crystals. In order to increase the crystallization yield, thesolution, after the crystal formation has substantially been finished,is cooled to a much lower temperature if necessary, and the formedcrystals are separated from the filtrate by a filter, washed and dried.Of course, it is also possible to apply decoloration treatment withactivated carbon, active clay, silica gel, etc. in the course of therecrystallization operation.

Thus, the present invention provides the hydroxyphenylpropionic acidester represented by the structural formula (I) having a novel and sofar unknown crystalline structure. Also, by producing said ester in theform of the δ-crystals of the present invention, the ester of thestructural formula (I), which has been difficult to obtain in highpurity on the commercial scale by conventional methods, can be producedin a high yield on a commercial scale without any disadvantage inoperation such as scaling of the apparatus, and in the form of whitecrystals superior in color, being quite satisfactory in both purity andpracticability.

The present invention will be illustrated with reference to thefollowing examples. The percentages (%) in the reference examples,examples and comparative examples are by weight unless otherwisespecified.

REFERENCE EXAMPLE 1

To a 500-ml four-necked flask equipped with a stirrer, condenser,thermometer and nitrogen-introducing pipe were added 200.3 g (0.8 mole)of methyl 3-(3-tertbutyl-4-hydroxy-5-methylphenyl)-propionate and 60.88g (0.2 mole) of3,9-bis(2-hydroxy-1,1-dimethylethyl)-2,4,8,10-tetraoxaspiro[5.5]undecane,and the mixture was formed into solution by heating at 150° C. for 30minutes with stirring in a nitrogen atomsphere. After adding 2.25 g(0.04 mole) of calcium oxide to this solution, the solution was heatedto 190° C. and kept at the same temperature for 6 hours while distillingoff formed methanol to complete the reaction.

After completion of the reaction, the reaction solution was diluted withtoluene, neturalized with aqueous dilute hydrochloric acid and washedwith water. After removing toluene by distillation, 97.1 g of methyl3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate, the startingmaterial present in excess, were distilled off to obtain 148.3 g of apale yellow highly viscous substance. Analysis of this highly viscoussubstance showed that it substance contained 96.4% of3,9-bis{2-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1-dimethylethyl}-2,4,8,10-tetraoxaspiro[5.5]undecane,the yield of this product being 96.5% based on3,9-bis(2-hydroxy-1,1-dimethylethyl)-2,4,8,10-tetraoxaspiro[5.5]undecane and also that said substance contained methyl3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate which was thestarting material, and other by-producs in the amounts of 1.2% and 2.4%,respectively.

This highly viscous substance, upon Cu-K.sub.α X-ray diffractionanalysis had an X-ray diffraction pattern as shown in FIG. 4 with noclear diffraction peak.

REFERENCE EXAMPLE 2

Procedure was carried out in the same manner as in Reference example 1except that 2.25 g (0.02 mole) of potassium tert-butoxide was used inplace of calcium oxide, and that reaction was completed at 150° C. undera pressure of 5 mmHg. The product was after-treated in the same manneras in Reference example 1. As a result, 92.5 g of methyl3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate, the startingmaterial present in excess, was recovered, and 145.2 g of a brown highlyviscous substance was obtained. Analysis of this highly viscoussubstance showed that it contained 87.5% of3,9-bis{2-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1-dimethylethyl}-2,4,8,10-tetraoxaspiro[5.5]undecane,the yield of this product being 85.8% based on3,9-bis(2-hydroxy-1,1-dimethylethyl)-2,4,8,10-tetraoxaspiro[5.5]undecane,and also that said substance contained methyl3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate which was thestarting material and other by-products in the amounts of 1.4% and11.1%, respectively.

REFERENCE EXAMPLE 3

Procedure was carried out in the same manner as in Reference example 1except that 0.46 g (0.02 mole) of lithium amide was used in place ofcalcium oxide, and that reaction was completed at 150° C. under apressure of 5 mmHg. the product was after-treated in the same manner asin Reference example 1. As a result, 95.4 g of methyl3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate, the startingmaterial present in excess, was recovered, and 145.8 g of a brown highlyviscous substance was obtained. Analysis of this highly viscous itshowed that said substance contained 88.9% of3,9-bis{2-[3-(3-tert-butyl-4-hydroxy-5-methylpheny)propionyloxy]-1,1-dimethylethyl}-2,4,8,10-tetraoxaspiro[5.5]undecane, the yield of this product being 87.5% basedon3,9-bis(2-hydroxy-1,1-dimethylethyl)-2,4,8,10-tetraoxaspiro[5.5]undecane,and also that said substance contained methyl3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate which was thestarting material and other by-products in the amounts of 1.5% and 9.6%,respectively.

The highly viscous substances obtained in Reference examples 2 and 3were subjected to Cu-K.sub.α X-ray diffraction, and had the same X-raydiffraction pattern as shown in FIG. 4.

EXAMPLE 1

Fifty grams of the highly viscous substance obtained in Referenceexample 1 were dissolved in 212.5 g of methanol at 60° C. The resultingsolution was cooled while adding 37.5 g of water with stirring, and 0.1g of seed crystals was added at 50° C. After stirring the solution atthe same temperature for further 2 hours to form crystals, the solutionwas cooled to 15° C. and stirred at the same temperature for 2 hours.The crytals obtained were filtered off on a glass filter, washed with amixture of 170 g of methanol and 30 g of water previously cooled to 15°C. and dried to obtain 45.7 g of white crystals having a melting pointof 124° C. to 126° C. Analysis of the white crystals showed that theycontained 98.0% of the desired3,9-bis{2-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1-dimethylethyl}-2,4,8,10-tetraoxaspiro[5.5]undecane,and also that said crystals contained methyl3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate which was thestarting material, and other by-products in the amounts of 0.7% and1.3%, respectively.

These white crystals were subjected to Cu-K X-ray diffraction to obtainan X-ray diffraction pattern with sharp diffraction peaks at angles ofdiffraction, 2θ=4.2° and 2θ=10.6°, as shown in FIG. 1.

EXAMPLES 2 TO 4

Recrystallization was repeated in the same manner as in Example 1 exceptthat the methanol/water mixture was replaced by the same weight of eachof 10% water-containing ethanol (Example 2), 10% water-containingisopropanol (Example 3) and 5% water-containing n-hexanol (Example 4).The results are shown in Table 3.

EXAMPLES 5 TO 7

Recrystallization was repeated in the same manner as in Example 1 exceptthat the highly viscous substance was dissolved at 100° C. and that themethanol/water mixture was replaced with the same amount of each of2-ethylhexanol only (Example 5), glycerin only (Example 6) andtriethylene glycol only (Example 7), and that the crystals were formedat 80° C. and washed with the respective solvents. The results are shownin Table 3.

EXAMPLES 8 TO 15

Recrystallization was repeated in the same manner as in Example 1 exceptthat the methanol/water mixture was replaced with the same weight ofeach of 50% water-containing acetone (Example 8), 30% water-containingmethyl isobutyl ketone (Example 9), 50% water-containing acetonitrile(Example 10), 50% water-containing dioxane (Example 11), 50%water-containing tetrahydrofuran (Example 12), 70% water-containingN,N-dimethylformamide (Example 13), 60% water-containingN,N-dimethylacetamide (Example 14) and 50% water-containing pyridine(Example 15). The results are shown in Table 3.

EXAMPLE 16

Fifty grams of the highly viscous substance obtained in Referenceexample 1 was disolved in 250 g of cyclohexane at 70° C. The resultingsolution was cooled with stirring, and 0.1 g of seed crystals were addedat 50° C. Thereafter, the solution was stirred at the same temperaturefor further 15 hours to form crystals. The resulting crystals werefiltered off at room temperature on a glass filter, washed withcyclohexane and dried at 40° C. under reduced pressure to obtain 46.0 gof white crystals having a melting point of 120° C. to 125° C. Analysisof the white crystals showed that they contained 98.5% of the desired3,9-bis{2-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1-dimethylethyl}-2,4,8,10-tetraoxaspiro[5.5]undecaneand 1.5% of by-products, but that there was contained no methyl3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate which was thestarting material.

EXAMPLES 17 AND 18

Recrystallization was repeated in the same manner as in Example 16except that the highly viscous substances obtained in Reference example2 (Example 17) and 3 (Example 18), respectively, were used in place ofthe highly viscous subtance obtained in Reference example 1. The resultsare shown in Table 3.

EXAMPLES 19 TO 21

Recrystallization was repeated in the same manner as in Example 16except that cyclohexane was replaced by each of methylcyclopentane(Example 19), methylcyclohexane (Example 20) and cyclooctane (Example21). The results are shown in Table 3.

EXAMPLE 22

Fifty grams of the highly viscous substance obtained in Referenceexample 1 were dissolved in 75 g of toluene at 70° C. The resultingsolution was cooled with stirring, and 0.1 g of seed crystals was addedat room temperature. Thereafter, the solution was stirred at the sametemperature for further 8 hours to form crystals. The solution was thencooled to -5° C. and stirred at the same temperature for further 2hours. The resulting crystals were filtered off on a glass filter,washed with cold toluene and dried under reduced pressure to obtain 43.0g of white crystals having a melting point of 122° C. to 125° C.Analysis of the white crystals showed that they contained 98.5% of thedesired3,9-bis{2-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1-dimethylethyl}-2,4,8,10-tetraoxaspiro[5.5]undecaneand 1.5% of by-products, but that there is contained no methyl3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate which was thestarting material.

EXAMPLES 23 TO 30

Recrystallization was repeated in the same manner as in Example 22except that 75 g of toluene was replaced by each of 100 g ofethylbenzene (Example 23), 150 g of cumene (Example 24), 150 g ofp-cymene (Example 25), a mixture of 50 g of ethyl acetate and 150 g ofn-hexane (Example 26), a mixture of 75 g of n-butyl acetate and 150 g ofn-hexane (Example 27), a mixture of 150 g of di-n-butyl phthalte and 100g of n-hexane (Example 28), a mixture of 50 g of chloroform and 150 g ofn-hexane (Example 29) and a mixture of 150 g of1,1,2,2-tetrachloroethane and 50 g of n-hexane (Example 30). Forwashing, the same solvents were used respectively. The results are shownin Table 3.

The white crystals obtained in the above Examples 2 to 30 were subjectedto Cu-K.sub.α X-ray diffraction to find that all the white crystals hadthe same X-ray diffraction pattern as shown in FIG. 1, and also thatsharp X-ray diffraction peaks were observed in all cases at angles ofdiffraction, 2θ=4.2° and 2θ=10.6°.

COMPARATIVE EXAMPLE 1

Recrystallization was carried out in the same manner as in Example 1except that the methanol/water mixture was replaced by the same weightof 30% water-containing methanol, and that the crystal formation wasconducted at 30° C. The result is shown in Table 3.

COMPARATIVE EXAMPLE 2

Recrystallization was carried out in the same manner as in Example 16except that the crystal formation was conducted at 30° C. The result isshown in Table 3.

COMPARATIVE EXAMPLE 3

Recrystallization was carried out in the same manner as in Example 17except that the crystal formation was conducted at 30° C. The result isshown in Table 3.

COMPARATIVE EXAMPLE 4

Recrystallization was carried out in the same manner as in Example 18except that the crystal formation was conducted at 30° C. The result isshown in Table 3.

COMPARATIVE EXAMPLE 5

Recrystallization was carried out in the same manner as in Example 16except that n-hexane was used in place of cyclohexane. The result isshown in Table 3.

In the above Comparative examples, the Cu-K.sub.α X-ray diffractionpatterns of the white crystals obtained in Comparative examples 1, 2 and5 were as shown in FIGS. 5, 2 and 3, respectively.

The white crystals obtained in Comparative examples 3 and 4 had the sameX-ray diffraction pattern as shown in FIG. 2.

In the drawings, FIG. 1 is the X-ray diffraction pattern of the novelcrystals (δ-crystal) of the present invention obtained in Example 1.FIGS. 2 and 3 are the X-ray diffraction patterns of the crystals(αβ-crystal) obtained in Comparative examples 2 and 5, respectively.FIG. 4 is the X-ray diffraction pattern of the highly viscous substance(γ-crystal) obtained in Reference example 1, and FIG. 5 is that of thecrystal (mixture of αβ-crystal and δ-crystal) obtained in Comparativeexample 1.

                                      TABLE 3                                     __________________________________________________________________________                 Purity of         Crystalli-                                                                          Time requi-                                     Weight of                                                                           desired           zation                                                                              red for   Melting                               crystal                                                                             product                                                                            Recrystallization                                                                          tempera-                                                                            crystalli-                                                                              point                                 (g)   (wt. %)                                                                            solvent      ture (°C.)                                                                   zation(hr)                                                                          Color                                                                             (°C.)                   __________________________________________________________________________    Example                                                                             1                                                                              45.7  98.0 Methanol/water                                                                             50    2     White                                                                             124-126                              2                                                                              45.3  97.8 Ethanol/water                                                                              50    2     White                                                                             123-125                              3                                                                              46.0  97.5 Isopropanol/water                                                                          50    2     White                                                                             123-125                              4                                                                              46.5  97.5 n-Hexanol/water                                                                            50    2     White                                                                             122-126                              5                                                                              46.8  97.8 2-Ethylhexanol                                                                             80    3     White                                                                             120-124                              6                                                                              46.6  97.3 Glycerin     80    3     White                                                                             120-123                              7                                                                              46.6  97.2 Triethylene glycol                                                                         80    3     White                                                                             120-125                              8                                                                              44.0  98.5 Acetone/water                                                                              50    3     White                                                                             123-126                              9                                                                              44.8  98.0 Methyl isobutyl ketone/                                                                    50    3     White                                                                             123-125                                          water                                                            10                                                                              43.7  98.2 Acetonitrile/water                                                                         50    3     White                                                                             123-125                             11                                                                              43.3  97.9 1,4-Dioxane/water                                                                          50    3     White                                                                             122-124                             12                                                                              44.5  97.5 Tetrahydrofuran/water                                                                      50    3     White                                                                             122-125                             13                                                                              44.2  98.1 N,N-dimethylformamide/                                                                     50    3     White                                                                             122-125                                          water                                                            14                                                                              44.7  98.2 N,N-dimethylacetamide/                                                                     50    3     White                                                                             121-124                                          water                                                       Example                                                                            15                                                                              42.8  97.9 Pyridine/water                                                                             50    3     White                                                                             120-123                             16                                                                              46.0  98.5 Cyclohexane  50    15    White                                                                             120-125                             17                                                                              40.5  97.3 Cyclohexane  50    15    White                                                                             120-124                             18                                                                              41.9  97.5 Cyclohexane  50    15    White                                                                             120-124                             19                                                                              46.2  97.1 Methylcyclopentane                                                                         50    15    White                                                                             119-124                             20                                                                              45.9  97.5 Methylcyclohexane                                                                          50    15    White                                                                             118-123                             21                                                                              46.1  98.0 Cyclooctane  50    15    White                                                                             119-125                             22                                                                              43.0  98.5 Toluene      Room tem-                                                                           8     White                                                                             122-125                                                       perature                                            23                                                                              43.5  98.0 Ethylbenzene Room tem-                                                                           8     White                                                                             121-125                                                       perature                                            24                                                                              43.9  97.7 Cumene       Room tem-                                                                           8     White                                                                             121-124                                                       perature                                            25                                                                              44.7  98.1 p-Cymene     Room tem-                                                                           8     White                                                                             120-124                                                       perature                                            26                                                                              45.0  97.4 Ethyl acetate/n-hexane                                                                     Room tem-                                                                           8     White                                                                             119-123                                                       perature                                       Example                                                                            27                                                                              44.1  97.3 n-Butyl acetate/                                                                           Room tem-                                                                           8     White                                                                             118-123                                          n-hexane     perature                                            28                                                                              45.6  97.2 Di-n-butyl phthalate/                                                                      Room tem-                                                                           8     White                                                                             119-123                                          n-hexane     perature                                            29                                                                              44.3  97.9 Chloroform/n-hexane                                                                        Room tem-                                                                           8     White                                                                             120-124                                                       perature                                            30                                                                              46.0  97.5 1,1,2,2-Tetrachloro-                                                                       Room tem-                                                                           8     White                                                                             118-124                                          ethane/n-hexane                                                                            perature                                       Compa-                                                                              1                                                                              44.3  97.8 Methanol/water                                                                             30    5     White                                                                             102-120                        rative                                                                              2                                                                              46.1  98.3 Cyclohexane  30    6     White                                                                             102-107                        example                                                                             3                                                                              37.6  93.5 Cyclohexane  30    24    Pale                                                                              95-99                                                                     yellow                                   4                                                                              39.4  93.8 Cyclohexane  30    24    Pale                                                                               95-100                                                                   yellow                                   5                                                                              48.0  96.7 n-Hexane     50     6.sup.A                                                                            Pale                                                                               93-101                                                                   yellow                             __________________________________________________________________________     *Solidified at the bottom of apparatus and did not disperse.             

What is claimed is:
 1. A method for producing hydroxyphenylpropionicacid ester represented by the structural formula, ##STR3## having acrystalline structure which, when subjected to Cu-K.sub.α X-raydiffraction, shows sharp X-ray diffraction peaks at angles ofdiffraction, 2θ=4.2° and 2θ=10.6°, which comprises dissolving thehydroxyphenylpropionic acid ester in(1) a recrystallization solventcomprising a water-soluble solvent and water in an amount of 0 to 3times by weight based thereon, or (2) a recrystallization solventcomprising a C₅ -C₁₀ alicyclic hydrocarbon,and maintaining the resultantsolution at a temperature of 40° C. or higher to form crystals of thehydroxyphenylpropionic acid ester.
 2. A method as claimed in claim 1,which further comprises cooling the solution after crystallization at atemperature of b 40° C. or higher.
 3. A method as claimed in claim 1,wherein the recrystallization solvent comprises a C₁ -C₃ alcohol andwater in an amount of 0 to 0.4 time by weight based thereon.
 4. A methodas claimed in claim 3, wherein the recrystallization solvent comprisesmethanol and water in an amount of 0 to 0.3 time by weight basedthereon.
 5. A method as claimed in claim 3, wherein therecrystallization solvent comprises isopropanol and water in an amountof 0 to 0.2 time by weight based thereon.
 6. A method as claimed inclaim 1, wherein the recrystallization solvent comprises a C₃ -C₆aliphatic ketone and water in an amount of 0 to 2 times by weight basedthereon.
 7. A method as claimed in claim 6, wherein therecrystallization solvent comprises acetone and water in an amount of 0to 2 times by weight based thereon.
 8. A method as claimed in claim 1,wherein the recrystallization solvent is cyclohexane.
 9. A method forproducing hydroxyphenylpropionic acid ester represented by thestructural formula, ##STR4## having a crystalline structure which, whensubjected to Cu-K.sub.α X-ray diffraction, shows sharp X-ray diffractionpeaks at angles of diffraction, 2θ=4.2° and 2θ=10.6°, which comprisesrecrystallizing the hydroxyphenylpropionic acid ester from arecrystallization solvent comprising a water-insoluble solvent otherthan alicyclic or aliphatic hydrocarbons and an aliphatic hydrocarbon inan amount of 0 to less than 10 times by weight based on thewater-insoluble solvent.